Invalidate user entry by using isnan or isempty function

Hi,

How do I invalidate a user entry if a positive number is required from the user but the user type a char or negative value.

when a user type a char or negative value,

a prompt will ask the user to reenter again.

% Check for erroneous input and prompt the user to enter option again

while conversion == 0

conv =str2double(conversion);

conversion = input("\nEnter an option. Yes or No \n", 's');

if isempty(conversion)

fprintf("Option Invalid");

conversion = input("\nEnter an option. DR or RD\n", 's');

elseif isnan(conv)

fprintf("Option Invalid");

conversion = input("Enter an option. DR or RD\n", 's');

elseif conv < 0

fprintf("Option Invalid");

conversion = input("Enter an option. DR or RD\n", 's');

end

end

Answer 1

[Jorg Woehl]

str2double returns NaN (not-a-number) when it cannot convert text to a number. You can therefore simply use isnan to test if a number has been entered, and combine that with a x>0 check:

str = input('Enter an option: ', 's');
x = str2double(str);
while isnan(x) || ~(x>0)
    str = input('Invalid input. Enter an option: ', 's');
    x = str2double(str);
end